The present invention relates to coating compositions based upon hydroxyl containing acrylic polymers and organopolysiloxanes.
U.S. Pat. No. 4,283,387 to Young et al is directed to a reversibly crosslinkable coating composition designed for the controlled release of bioactive agents, more particularly to the controlled release of pesticides. The coating composition comprises a mixture of a carbinol containing polymer, crosslinking agents for said polymer consisting essentially of a hydrolyzable silane or an organopolysiloxane containing hydrolyzable silane groups, and a hydrolyzable organic titanium compound and a pesticide. Since these coating compositions are reversibly crosslinked, the crosslinking is capable of breaking down to release the bioactive agent. Moreover, the amount of organopolysiloxane and carbinol containing polymer is such that the organopolysiloxane is present in relatively small amounts as compared to the carbinol containing polymer.
U.S. Pat. No. 4,103,065 to Gagnon is directed to improved coating compositions for polycarbonate or acrylic articles. The improvement in the composition of the Gagnon invention resides in the addition of constituent (c) to constituents (a) and (b) which are organopolysiloxane partial condensate product resin and an alkylated melamine formaldehyde partial condensate resin, respectively. The additional constituent (c) is a composition containing specified percentages of linear diol, thermosetting acrylic and crosslinking agent. The Gagnon composition specifically requires that the thermosetting acrylic contain from about 4 to about 10 percent by weight of the acrylic of a hydroxyalkyl ester of an alpha,beta-unsaturated carboxylic acid.
The art recognized compositions such as those of Gagnon which have been detailed above have been deficient in that they have been unable to provide the proper balance of flexibility and durability. Coating compositions based predominantly upon the type of polysiloxanes which are detailed in Gagnon tend to be much too brittle. Attempts to flexibilize these compositions has tended to make them less brittle, although not as durable as might be desired.
In contrast to the above, the coating compositions provided by the present invention show unexpected advantages both in flexibility and durability.